Conventionally semiconductor wafers are diced using mechanical sawing after manufacturing of semiconductor structures on the wafer. This technique has the disadvantage that due to the kerf width, a considerable portion of the semiconductor material is wasted as dust. According to some estimates, this means at least hundreds, if not thousands of tons of silicon waste annually in the global scale.
Also laser light can be used for dicing of semiconductor wafers after manufacturing of semiconductor structures on the wafer. Generally, in such methods, a cutting line is produced by laser to the wafer after which the wafer is cut along the cutting line. Several methods have been proposed for this.
EP 1338371 discloses a method wherein a pulse laser beam is radiated on a predetermined cutting line on a surface of a workpiece under conditions causing multiple photon absorption. The focal point of the laser is kept inside the workpiece and moved for forming a modified area inside the workpiece. In the publication, there is described a method utilizing Nd:YAG pulsed laser at 100 kHz, the laser having a wavelength of 1064 nm and spot cross-sectional area of 3.14*10−8 cm2. The pulse width is 30 ns and the moving speed of a mounting table having the object to be processed is 100 mm/s. Thus, laser-induced spots are located in line and next to each other within the substrate.
Gattrass et al. disclose in Nature Photonics, Vol. 2, April 2008, pp 219-225 a femtosecond laser micromachining method for transparent materials. The method is aimed at manufacturing waveguides, active optical devices, microfluidic devices and filters and resonators, achieving polymerization, bonding of materials, and performing nanosurgery. In the method, femtosecond-scale laser pulses are directed to the substrate material at a power range causing nonlinear absorption within the substrate. Another method for femtosecond processing is disclosed by Miyamoto et al. in Journal of Laser Micro/Nanoengineering Vol. 2, No. 1, 2007.
Miyamoto et al. disclose in Proceedings of the 4th International Congress on Laser Advanced Materials Processing a method of local melting of glass material and its application to direct fusion welding. The publication discloses an examples in which picosecond-scale laser pulses are directed to the surface of borosilicate glass and to the interior of fused silica. In the examples, a pulse width of 16 ps with a frequency of 1 kHz were used, the traveling velocity of the substrate being 0.5, 5 or 10 mm/s. On the other hand, pulses having a duration of 10 ps were used at frequencies of 100 and 500 kHz and The publication suggests that the efficiency of fusion welding directly depends on the increase of nonlinear absorption the laser pulses to the substrate. Moreover, it has been suggested that increasing the pulse energy increases nonlinear absorption and thus welding efficiency.
Despite the many advantages of the abovementioned techniques, there is a need for even more efficient laser processing techniques. In particular, increasing the pulse energy is not possible above certain levels due to practical limitations set by the instrumentation and the tolerance of substrate materials of momentary pulse energies. Excessive irradiance will induce shock waves into material and cause micro level cracks.